Optical head and optical data recording and reproducing apparatus having the same

ABSTRACT

An optical head for reproducing data from first and second optical disks which are different from each other in at least one of a base material thickness and an available wavelength, includes: a first light source for emitting a first light beam, the first light beam being used for reproducing data from the first optical disk: an optical system designed to converge the first light beam onto the first optical disk in accordance with a base material thickness and an available wavelength of the first optical disk: and a second light source for emitting a second light beam, the second light beam being used for reproducing data from the second optical disk, wherein an optical path length between the second light source and the optical system is different from an optical path length between the first light source and the optical system, and wherein the optical system converges the second light beam onto the second optical disk.

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention relates to an optical head, and more particularlyto an optical head capable of recording/reproducing data to and from avariety of optical disks each having a different available wavelength ora base material of different thicknesses.

2. Description of the Related Art:

A standard optical head using a laser diode (LD) is described withreference to FIG. 20. A light beam 203 output from an LD 201 iscollimated by a collimate lens 202. The collimated light beam 203, whichis a P-polarized light beam, is transmitted through a polarized beamsplitter 204 (hereinafter, referred to as "PBS"), and then is incidentonto a quarter-wave plate 205. The light beam 203 output from thequarter-wave plate 205 is, via a reflecting mirror 206, incident onto anobjective lens 207. The light beam 203 is converged into an imagingpoint p by the objective lens 207, thus forming a beam spot 209 on therecording face of an optical disk 208. Then, a light beam 210, i.e., thelight beam 203 reflected by the optical disk 208, is incident onto theobjective lens 207 again. After passing though the reflecting mirror 206and the quarter-wave plate 205 in this order, the light beam 210 isincident onto the PBS 204. At this stage, the light beam 210 has changedinto an S-polarized beam by the quarter-wave plate 205 and is reflectedby the PBS 204 without transmitting therethrough. The reflected lightbeam 210 passes through a detection lens 211 and a cylindrical lens 212,and is incident onto a photodetector (hereinafter referred to as "PD")213. The PD 213 detects a reproducing signal based on the incident lightbeam 210. At the same time, the PD 213 detects a focus control signaland a tracking control by using known methods. For example, the focuscontrol signal is obtained by an astigmatism method, and the trackingcontrol signal is obtained by a push-pull method.

The objective lens 207 used in such an optical head is designed inconsideration of the thickness of the base material of the optical disk208 and the available wavelength thereof. This is because a wave-frontaberration arises if the base material thickness or available wavelengthof the optical disk 208 is different from the base material thickness oravailable wavelength, a factor which is considered in designing theobjective lens 207, a factor which can result in failure of therecording/reproducing operation.

Conventionally, the base materials of a compact disk (hereinafter,referred to as "CD"), a video disk, an optical disk used for amagneto-optic disk drive, etc., all have been 1.2 mm in thickness. Inaddition, the wavelength of a light beam used for therecording/reproducing operation of such optical disks (hereinafter,referred to as "the available wavelength") has been 780 nm to 830 nm.Accordingly, as for the conventional optical disk, optical disks ofvarious types can be recorded and reproduced by using the same opticalhead.

In recent years, in order to realize an optical disk with a higherrecording density, attempts have been made to increase the numericalaperture of the objective lens, to use a light beam of a shorterwavelength, and the like. However, it is difficult to perform therecording/reproducing operation of the high density recording opticaldisk using an optical head identical with that used for the conventionaloptical disk.

First, by increasing the numerical aperture of the objective lens, thewider frequency band allowing the light beam to be reproduced isrealized due to improvement in the optical resolution. However, in sucha case, if the recording face of the optical disk 208 is inclined withrespect to the plane perpendicular to the optical axis of the objectivelens 207, the come of the light spot 209 increases. Thus, the increaseof the numerical aperture of The objective lens does not actuallyimprove the image forming efficiency.

In order to increase the numerical aperture of the objective lenswithout increasing the coma aberration, an optical disk having a thinnerbase material may be used. FIG. 21 is a graph showing the correlationbetween the thickness of the base material of the optical disk 208 andthe numerical aperture of the objective lens 207. The curve in FIG. 21is constituted by the points at which the peak value of the lightintensity distribution of the light spot 209 is a predetermined valuewhen the recording face of the optical disk 208 is inclined by 0.2° fromthe plane perpendicular to the optical axis of the objective lens 207.

As seen from FIG. 21, the decline of the peak value due to theinclination of the optical disk 208 in the case where the beam spot 209is formed by the objective lens 207 with a numerical aperture of 0.5 onthe optical disk whose base material is 1.2 mm thick is substantiallyequal to that in the case where it is formed by the objective lens 207with a numerical aperture of 0.62 on the optical disk whose basematerial is 0.6 mm thick. Accordingly, even if the numerical aperture ofthe objective lens 207 increases, by making the base material of theoptical disk thinner, the coma resulting from the inclination of theoptical disk can be reduced so as to be in the same degree as the comeof the conventional disk. However, when making the base material of theoptical disk thinner, the wave-front aberration makes it impossible touse the same optical head to perform the recording/reproducingoperations for the optical disks having the base material of 1.2 mm inthickness and those having thinner base material. That is,interchangeability between optical heads is lost. As a result, in orderto perform the recording/reproducing operations for optical disks havinga base material of 1.2 mm in thickness and those having a thinner basematerial by one optical data recording/reproducing apparatus, theoptical data recording/reproducing apparatus is required to have twodifferent optical heads, one for the optical disk of the formerthickness and the other for that of the latter thickness.

Second, in the case of applying a light beam with a shorter wavelengthfor the recording/reproducing operation, an improved optical resolutionallows the widening of the frequency band assuring the recording orreproducing operation. However, for the purpose of reproducing data froma conventional optical disk whose available wavelength is 780 nm, if alight beam of a shorter wavelength, e.g., 635 nm, is used, areproduction signal or control signals of a sufficient level cannot beobtained due to the difference in the reflectance or absorption rate ofthe recording face of the optical disk. This problem is prominent, forexample, when using a light beam of a short wavelength for a CD-Rstandardized as a writable CD.

FIG. 22 is a graph showing exemplary data representing how thereflectance of the CD-R depends on the wavelength of the light beam. TheCD-R is defined as having a reflectance of 65% or more with respect to alight beam having a wavelength of 775 nm to 820 nm. However, thereflectance is extremely lowered as for a light beam having a wavelengthout of this range. In some types of CD-R, the reflectance becomes assmall as 5% with respect to a light beam having a wavelength of about635 nm. Furthermore, the reproduction power of the CD-R is defined to be0.7 mW or less. As a result, when trying to reproduce data from the CD-Rhaving the wavelength dependency of the reflectance as shown in FIG. 22by an optical head with an LD generating a light beam of a wavelength of635 nm, even assuming that the reproduction power is the upper limitvalue of 0.7 mW and that the efficiency of a reproduction optical systemis 100%, only a power of 35 μW is obtainable in thereproduction-detection system. Thus, in order to perform therecording/reproducing operation of the CD-R whose available wavelengthis 780 nm by using the light beam of a wavelength of 635 nm, a signalreproducing system which has an extremely high S/N ratio is required andthus is expensive.

However, in consideration of the fabrication cost, an optical head of awidely marketed standard model is desired to have a reproduction systemwith an efficiency of 50% or less. Hence, it is difficult for theoptical head of a standard model to assure a satisfactory reproductionS/N ratio, when using the light beam of a wavelength of 635 nm.

For these reasons, it has been very difficult to use a single opticalhead to perform the recording/reproducing operation for both thehigh-density optical disk available for a light beam of a wavelength of635 nm and the conventional optical disk available for a light beam of awavelength of 780 nm. Accordingly, in order to perform therecording/reproducing operation for both the high-density optical diskand the conventional optical disk by a single optical datarecording/reproducing apparatus, the apparatus has been required toseparately provide the optical head using a light beam having awavelength of 635 nm and the optical head designed for conventionaloptical disks. In addition, the apparatus has needed to provide opticalsystems respectively for both optical heads, for appropriatelyconverging a light beam generated from each of the LDs onto the opticaldisk. This bulky configuration has necessitated high fabrication costs,as well as hindering the apparatus from being developed into asmaller-size.

SUMMARY OF THE INVENTION

According to one aspect of the invention, the optical head forreproducing data from first and second optical disks which are differentfrom each other in at least one of a base material thickness and anavailable wavelength, includes: a first light source for emitting afirst light beam, the first light beam being used for reproducing datafrom the first optical disk; an optical system designed to converge thefirst light beam onto the first optical disk in accordance with a basematerial thickness and an available wavelength of the first opticaldisk; and a second light source for emitting a second light beam, thesecond light beam being used for reproducing data from the secondoptical disk, wherein an optical path length between the second lightsource and the optical system is different from en optical path lengthbetween the first light source and the optical system, and wherein theoptical system converges the second light beam onto the second opticaldisk.

According to another aspect of the invention, the optical data recordingand reproducing apparatus includes an optical head for reproducing datafrom first and second optical disks which are different from each otherin at least one of a base material thickness and an availablewavelength, disk discriminating means for discriminating between thefirst and second optical disks, and drive means for driving the opticalhead based on a result of the discrimination obtained by the diskdiscriminating means, the optical head including: a first light sourcefor emitting a first light beam, the first light beam being used forreproducing data from the first optical disk; an optical system designedto converge the first light beam onto the first optical disk inaccordance with a base material thickness and an available wavelength ofthe first optical disk; and a second light source for emitting a secondlight beam, the second light beam being used for reproducing data fromthe second optical disk, wherein an optical path length between thesecond light source end the optical system is different from an opticalpath length between the first light source and the optical system, endthe optical system is determined so that the second light beam isconverged onto the second optical disk.

Thus, the invention described herein makes possible the advantage ofproviding a compact and inexpensive optical head and an optical datarecording and reproducing apparatus capable of performing therecording/reproducing operation of optical disks which are different inat least one of the thickness of the base material and the availablewavelength by using one optical system common to the both optical disks.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 2A and 2B are schematic diagrams each showing theconfiguration of an optical head according to the present invention.

FIGS. 3A and 3B are graphs each showing the relationship between thedistance from an LD and a collimate lens and a wavefront aberration.

FIG. 4 is a side view showing a first example of the present invention.

FIG. 5 is a side view showing a modification of the first example of thepresent invention.

FIG. 6 is a side view showing a second example of the present invention.

FIG. 7 is a side view showing a third example of the present invention.

FIGS. 8A and 8B are side views each showing a fourth example of thepresent invention.

FIGS. 9A and 9B are diagrams each showing the relationship between thetransmittance and the wavelength of the wavelength polarization filter.

FIG. 10 is a block diagram showing an optical head of the fourth exampleof the present invention.

FIGS. 11A and 11B are side views each showing a fifth example of thepresent invention.

FIGS. 12A and 12B are side views each showing a sixth example of thepresent invention.

FIGS. 13A and 13B are side views each showing a seventh example of thepresent invention.

FIGS. 14A and 14B are side views each showing an eighth example of thepresent invention.

FIG. 15 is a diagram schematically showing the configuration of alaser-detector integrated module.

FIG. 16 is a cross-sectional view showing a pattern of a gratingprovided in the laser-detector integrated module shown in FIG. 15.

FIGS. 17A and 17B are side views each showing a ninth example of thepresent invention.

FIGS. 18A and 18B are side views each showing a tenth example of thepresent invention.

FIGS. 19A and 19B are diagrams each showing the relationship between thetransmittance and the wavelength of the wavelength polarization filter.

FIG. 20 is a side view showing an exemplary configuration of aconventional optical head.

FIG. 21 is a graph showing the relationship between the base materialthickness of an optical disk and the numerical aperture of an objectivelens.

FIG. 22 is a graph showing the wavelength dependency of the reflectanceof a CD-R.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, the present invention is described from the viewpoint of theinterchangeability between optical disks each having a base material ofa different thickness. FIGS. 1A and 1B are diagrams showing theschematic structure of an optical head capable of performing arecording/reproducing operation for both of an optical disk having abase material thinner than conventional ones (hereinafter, referred toas "a thin optical disk") and an optical disk having a base material ofa conventional thickness (1.2 mm). Herein, it is assumed that theavailable wavelength of the thin optical disk and that of the opticaldisk of the conventional base material thickness are substantially thesame.

The optical head shown in FIGS. 1A and 1B includes a laser diode (LD)301a for the thin optical disk, an LD 301b for the optical disk havingthe conventional base material thickness, an LD drive circuit 320 fordriving these LDs and a disk discriminator 330. When an optical disk isset in the apparatus, the disk discriminator 330 judges whether the setoptical disk is the thin optical disk or the optical disk of a basematerial thickness of 1.2 mm. Based on the result of the judgment, theLD drive circuit 320 supplies a current to the LD corresponding to theset optical disk. In the case where the set optical disk is a thinoptical disk 308a, a current is supplied to the LD 301a for a thinoptical disk, as shown in FIG. 1A. The light beam 303a output from theLD 301a is focused on the thin optical disk 308a by means of aconverging optical system. On the other hand, in the case where the setoptical disk is an optical disk 308b whose base material is 1.2 mmthick, a current is supplied to the LD 301b for the optical disk 308b,as shown in FIG. 1B. Thus, a light beam 303b output from this LD 301b isconverged on the optical disk 308b. In both cases, the light beam 303aor 303b is reflected by the optical disk 308a or 308b. By means of ahalf mirror or the like disposed in the optical path between theconverging optical system and the LDs 301a end 301b, the optical path ofthe reflected light beam 310a or 310b is bent, so that the light beam310a or 310b is incident onto a PD 313. Based on the reflected lightbeam 310a or 310b, the PD 313 detects a reproduction signal, a focuscontrol signal and a tracking control signal. In the example shown inFIGS. 1A end 1B, the focus control signal is obtained by a phasedifference method, and the tracking control signal is obtained by apush-pull method. The light spot on the optical disk 308a or 308b iscontrolled so as to follow the track on which the data to be read isreceded, in accordance with these control signals.

Herein, the converging optical system is designed in accordance with theavailable wavelength and the base material thickness of the thin opticaldisk 308a. Because of this, when the light beam is converged on theoptical disk 308b whose base material is 1.2 mm thick, e wavefrontaberration arises on the recording face of the optical disk 308b. Thiswavefront aberration should be reduced to such a low level so as to benegligible in reproducing the data from the optical disk 308b. For thispurpose, in the optical head of the present invention, the LD 301b forthe optical disk 308b is located at a position such that the length ofoptical path between the LD 301b for the optical disk 308b and theconverging optical system is different from that between the LD 301a forthe thin optical disk 308a and the converging optical system. Theprocess of determining the optical path length between the LD 301b forthe optical disk 308b and the converging optical system will bedescribed in detail later.

Though only one PD is provided in the apparatus shown in FIGS. 1A and1B, in the case where a focus control signal is detected by anastigmatism method or a spot size detection (SSD) method, the PD isrequired to be provided in each of the LDs.

Next, with reference to FIGS. 2A and 2B, the present invention will bedescribed from the view-point of the interchangeability be%ween opticaldisks whose available wavelengths are different from each other. FIGS.2A and 2B are diagrams showing the schematic structure of an opticalhead of the present invention, which is capable of performing arecording/reproducing operation for both an optical disk whose availablewavelength is shorter than the conventional one (hereinafter, referredto as "the short wavelength available optical disk") and a conventionaloptical disk (whose available wavelength is 780 nm). Herein, it isassumed that the conventional optical disk is a CD-R in which thedependence of a reflectivity on the wavelength is especially high, andthat the base material thickness of the short wavelength availableoptical disk is the same as that of the conventional optical disk, i.e.,1.2 mm.

Similar to the optical head shown in FIGS. 1A and 1B, the optical headshown in FIGS. 2A and 2B includes a short wavelength LD 301a, a 780 nmLD 301b for the conventional optical disk 308b, an LD drive circuit 320for driving these LDs and a disk discriminator 330. When an optical diskto be recorded or reproduced is set in the optical data recording andreproducing apparatus, the disk discriminator 330 judges whether the setoptical disk is the short wavelength optical disk 308a or theconventional optical disk 308b. Based on the result of the judgment, theLD drive circuit 320 supplies a current either to the short wavelengthLD 301a or the 780 nm LD 301b. In the case where the set optical disk isthe optical disk 308b whose available wavelength is shorter then 780 nm,a current is supplied to the short wavelength LD 301a as shown in FIG.2A. The output light beam 303a is focused on the short wavelengthoptical disk 308a by means of e converging optical system. On the otherhand, in the case where the set optical disk is the CD-R 308b, a currentis supplied to the 780 nm LD 301b, as shown in FIG. 2B. Then, the lightbeam 303b having a wavelength of 780 nm is focused on the CD-R 308b. Inboth cases, the light beam 303a or 303b is reflected by the optical disk308a or 308b. The reflected beam 310a or 310b passes through aconverging optical system, and then, by means of a half mirror or thelike disposed between the converging optical system and the LDs 301a and301b, the reflected beam 310a or 310b is turned to a PD 313. Finally,the light beam is incident onto the PD 313. The PD 313 detects areproduction signal, a focus control signal and a tracking controlsignal based on the reflected light beam 310a or 310b. In the exampleshown in FIGS. 2A and 2B, the focus control signal is detected by aphase difference method, and the tracking control signal by a push-pullmethod. By using these control signals, a control for making the lightspot on the optical disk 308a or 308b follow the track is performed.

Herein, the converging optical system is designed in accordance with theavailable wavelength and base material thickness of the short wavelengthoptical disk 308a. Because of this, if the light beam 301b having awavelength of 780 nm is converged on the CD-R 308b, a wavefrontaberration arises on the recording face of the CD-R 308b. Thus, in theoptical head of the present invention, the above-mentioned wavefrontaberration on the recording face of the CDR 308b is compensated for bymaking the optical path length between the 780 nm LD 301b and theconverging optical system different from that between the shortwavelength LD 301a and the converging optical system. In this way, thewavefront aberration on the recording face of the CD-R 308b can bereduced to such a low level so as to be negligible in reproducing datafrom the CD-R.

In the foregoing, the case where the optical disks are different in thebase material thickness and the case where the optical disks aredifferent in the available wavelength have been discussed separatelyfrom each other. However, the present invention can be applied also tothe case where the optical disks are different both in the base materialthickness and the available wavelength. Also in this case, a convergingoptical system is designed in accordance with the base material and theavailable wavelength of a first optical disk (for example, an opticaldisk having a thin base material), and the LD for a second optical diskis disposed so that the optical path between the LD for the secondoptical disk and the converging optical system is different from thatbetween the LD for the first optical disk and the converging opticalsystem. This arrangement makes it possible to reproduce data from boththe first and second optical disks which are different from each otherboth in the base material thickness and in the available wavelength.

Hereinafter, the manner of determining the optical path length betweenthe converging optical system, designed in accordance with the basematerial thickness and the available wavelength Of one optical disk (thefirst optical disk), and the LD for the other optical disk (the secondoptical disk) will be described.

The converging optical system is designed to appropriately converge thelight beam 303a on the recording face of the first optical disk 308a, inaccordance with the base material thickness and the available wavelengthof the first optical disk 308a. Herein, the light beam 303a is soconverged as to make the wavefront aberration on the recording face ofthe first optical disk 308a 10 mλ (rms) or less. The optical path lengthbetween the LD 301b for the second optical disk 308b and the thusdesigned converging optical system is determined so as to minimize thewavefront aberration arising when the light beam 303b output from the LD301b is converged onto the recording face of the second optical disk308b by the converging optical system.

For example, the case where the base material thickness and theavailable wavelength of the first optical disk 308a are 0.6 mm and 635nm, respectively will be explained hereinafter. The base materialthickness and the available wavelength of the second optical disk 308bare 1.2 mm and 780 nm, respectively. The converging optical systemincludes a collimate lens (not shown) and the objective lens 317, and isdesigned to converge the light beam 303a from the LD 301a on the firstoptical disk 308a with a wavefront aberration of 10 mλ (rms) or less. Inthis case, the focal length of the collimate lens (not shown) and thatof the objective lens 317 are 3 mm and 25 mm, respectively.

FIG. 3A shows the relationship between the optical path length betweenthe LD 301b for the second optical disk 308b and the thus designedconverging optical system and the wavefront aberration arising when thelight beam 303b output from the LD 301b is converged onto the recordingface of the second optical disk 308b whose base material thickness is1.2 mm. As is apparent from this graph, the wavefront aberration recordsits minimum value, less then 10 mλ (rms), when the optical path lengthbetween the LD 301b and the collimate lens in the converging opticalsystem is about 17 mm. Accordingly, when the LD 301b is disposed at aposition such that the distance to the collimate lens becomes 17 mm, thereproducing operation of the second optical disk 308b can be performedwithout any problem, even if using the converging optical systemdesigned in accordance with the base material thickness and theavailable wavelength of the first optical disk 308a.

Next, the determination of the optical path length between theconverging optical system and each of the LDs in the case where thefirst optical disk 308a and the second optical disk 308b have the samebase material thickness and have different available wavelengths isexplained. The available wavelengths of the first and second opticaldisks 308a and 308b are 635 nm and 780 nm, respectively. The convergingoptical system including the collimate lens and the objective lens 317is designed to converge the light beam 303a having a wavelength of 635nm on the first optical disk 308a with a wavefront aberration of 10 mλ(rms) or less. The focal length of the collimate lens and the objectivelens are set to be 3.7 mm and 22.5 mm, respectively.

FIG. 3B shows the relationship between the optical path length betweenthe second LD 301b and the thus designed converging optical system andthe wavefront aberration arising when the light beam 303b output fromthe LD 301b is converged onto the second optical disk 308b. As isapparent from this graph, the wavefront aberration records its minimumvalue, less than 10 mλ (rms), when the optical path length between theLD 301b and the collimate lens in the converging optical system is about21.8 mm. Accordingly, when the LD 301b is disposed at a position suchthat the distance therefrom to the collimate lens becomes 21.8 mm, thereproducing operation of the second optical disk 308b can be performedwithout any problem, even if using the converging optical systemdesigned in accordance with the base material thickness and theavailable wavelength of the first optical disk 308a.

In the foregoing, the manner of determining the optical path lengthbetween the second LD and the converging optical system has beendescribed, with respect to the case where the first end second opticaldisks are different both in the base material thickness and theavailable wavelength, and the case where they have the same basematerial thickness but are different in the available wavelength.However, also in the case where they have the same available wavelengthbut are different in the base material thickness, the optical pathlength between the LD for the second optical disk end the convergingoptical system is determined in a similar manner.

With reference to FIGS. 1A through 2B, a general concept of the opticalhead according to the present invention has been described. However, theoptical head is actually configured in different ways depending on thevarious combinations of the base material thickness and the availablewavelength between the first and second optical disks. The actualconfigurations of the optical head will be described hereinafter, withreference to accompanying drawings.

EXAMPLE 1

Now, Example 1 of the present invention will be described with referenceto FIG. 4. In Example 1, the first optical disk 148a and the secondoptical disk 148b are different from each other both in the basematerial thickness and the available wavelength. FIG. 4 shows theconfiguration of an optical head including an LD 141a for a thin opticaldisk 148a and an LD 141b for a conventional optical disk, i.e., an LDwhich emits light of 780 nm. Herein, the conventional optical disk 148bis a compact disk (CD), and the available wavelength of the thin opticaldisk 148a is shorter than that of the CD.

In FIG. 4, a light beam 143a output from an LD 141a for a thin opticaldisk passes through a half mirror 146 and is collimated by a collimatelens 142. The light beam 143a output from the LD 141a is an S-polarizedbeam. After being collimated, the light. beam 143a is reflected by apolarization beam splitter (hereinafter, referred to as "PBS") 144.Subsequently, the light beam 143a is converted into a circularlypolarized beam by passing through a quarter-wave plate 145, and isincident on an objective lens 147. The objective lens 147 converges thelight beam 143a into an imaging point p on the recording face of a thinoptical disk 148a. Thus, a beam spot 149a is formed on the recordingface of the thin optical disk 148a.

Following this, a light beam 150a, which is the light beam 143areflected by the optical disk 148a, repasses through the objective lens147 and the quarter-wave plate 145 in this order. At this time, thelight beam 150a is incident on the PBS 144. The light beam 150atransmits through the PBS 144, since it has been converted into aP-polarized beam by the function of the quarter-wave plate 145. Thelight beam 150a transmitted through the PBS 144 is, via a cylindricallens 152 and a diaphragm lens 151, incident onto a wavelength selectingmirror 154. As the wavelength selecting mirror 154, this optical headprovides such an element as transmitting the light beam output from theLD 141a for a thin optical disk and reflecting the light beam outputfrom the LD 141b for a CD, i.e., the light beam of a wavelength of 780nm. Accordingly, the reflected light beam 150a transmits through thewavelength selecting mirror 154 and is incident on a PD 153a for a thinoptical disk. The PD 153a is configured so as to detect a focus controlsignal end a tracking control signal by an astigmatism method and apush-pull method, respectively, as well as a reproduction signal.

Next, the case where the optical disk set in the optical head shown inFIG. 4 is a CD will be described. A light beam 143b having a wavelengthof 780 nm is output from an LD 141b for a CD. Herein, the light beam143b output from the LD 141b is an S-polarized beam. The optical path ofthe light beam 143b is turned by the half mirror 146, so that the lightbeam 143b is incident onto the collimate lens 142. The light beam 143b,substantially collimated by the collimate lens 142, is reflected by thePBS 144. Subsequently, the light beam 143b is converted into acircularly polarized beam by passing through the quarter-wave plate 145,and thereafter is incident on the objective lens 147. The objective lens147 converges the light beam 143b into an imaging spot p' on therecording face of the CD 148b. Thus, a beam spot 149b is formed on therecording face of the CD 148b.

Following this, a light beam 150b, which is the light beam 143breflected by the optical disk 148a, repasses through the objective lens147 and the quarter-wave plate 145 in this order, and is incident on thePBS 144. At this time, the light beam 150b transmits through the PBS144, since it has been converted into a P-polarized beam by the functionof the quarter-wave plate 145. The light beam 150b transmitted throughthe PBS 144 passes through the cylindrical lens 152 and the diaphragmlens 151, and is incident onto a wavelength selecting mirror 154. Asdescribed above, the wavelength selecting mirror 154 reflects the lightbeam of a wavelength of 780 nm. The light beam 150b reflected by thewavelength selecting mirror 154 is incident onto a PD 153b for a CD.Similar to the above-mentioned PD 153a for a thin optical disk, the PD153b detects a focus control signal and a tracking control signal by anastigmatism method and a push-pull method, respectively, as well as areproduction signal.

In the configuration as shown in FIG. 4, each of the optical componentsof the converging optical system between the half mirror 146 and theobjective lens 147, as well as the cylindrical lens 152 end thediaphragm lens 151 are designed in accordance with the base materialthickness and the available wavelength of the thin optical disk 148a.Hence, in order to correct a wavefront aberration occurring when thelight beam 143b of a wavelength of 780 nm is focused on the CD 148b bythe thus designed optical components, the optical head of Example 1 isarranged so that optical path length between the LD 141b for a CD andthe half mirror 146 is different from the optical path length betweenthe LD 141a for a thin optical disk and the half mirror 146, asdescribed above with reference to FIG. 3A. As a result, the degree inwhich the light beam 143b converges on the recording face of the CD 148bcan be improved to a level sufficiently high enough for reproducing datafrom the CD.

In the above-described optical head, the available wavelength of thethin optical disk 148a and that of the CD 148b are different. Thepresent invention can be applied also to the case where they are thesame wavelength. However, in the case where the available wavelength ofthe thin optical disk 148a and that of the CD 148b are the same, thatis, the case where both of the available wavelengths are 780 nm, a halfmirror is used in place of the wavelength selecting mirror 154.

Furthermore, in the optical head shown in FIG. 4, in the case ofdetecting a focus control signal by a phase difference method, there isno necessity of providing one PD for each of the LDs. Instead, it issufficient to remove the wavelength selecting mirror 154 and provide onePD 153c, as shown in FIG. 5. However, in such a case, a signal obtainedfrom the PD 153c should be subjected to an appropriate correctingprocessing by a signal processing circuit (not shown).

EXAMPLE 2

Now, Example 2 of the present invention is described with reference toFIG. 6. In Example 2, the base material thickness of a first opticaldisk 168a is different from that of a second optical disk 168b. Thefirst optical disk and the second optical disk are a thin optical diskand a conventional optical disk, respectively. Similar to the opticalheads shown in FIGS. 4 and 5, an optical head shown in FIG. 6 includesan LD 161a for the thin optical disk 168a and an LD 161b for theconventional optical disk 168b, i.e., a 780 nm LD. In this example, theconventional disk 168b is a CD.

First, the case where the optical disk set in the optical head is a thinoptical disk 168a will be described hereinafter. A light beam 163aoutput from the LD 161a is incident onto a PBS 166. The LD 161a outputsa P-polarized beam as the light beam 163a. Accordingly, the light beam163a transmits through the PBS 166 and is incident on a collimate lens162. The light beam 163a collimated by the collimate lens 162 isincident on a half mirror 164. Then, the component of the light beam163a, reflected by the half mirror 164, are incident on an objectivelens 167. The light beam incident on the objective lens 167 is convergedinto an imaging point p on the recording face of the thin optical disk168a. Thus, a beam spot 169a is formed on the recording face of the thinoptical disk 168a.

Thereafter, a light beam 170a, i.e., the light beam reflected by theoptical disk 168a, repasses through the objective lens 167 and isincident on the half mirror 164. The component transmitting through thehalf mirror 164 passes through a cylindrical lens 172, a focusing lens171 and another PBS 174 in this order, to be incident onto a PD 173a fora thin optical disk 168a. The PD 173a is configured so as to detect afocus control signal and a tracking control signal by an astigmatismmethod and a push-pull method, respectively, as well as a reproductionsignal.

On the other hand, in the case where the optical disk set in the opticalhead is the CD 168b, a light beam 163b is output from an LD 161b for aCD. This LD 161b is disposed so as to output a linearly polarized beamwhose polarization direction is substantially perpendicular to that ofthe light beam 163a from the LD 161a. That is, the LD 161b for the CD168b outputs an S-polarized beam as the light beam 163b. The light beam163b passes through a cover glass 175, and then is incident onto the PBS166. The cover glass 175 is disposed between the PBS 166 and the LD 161bso as to correct the optical path length from the PBS 166 to the LD161b. Since the light beam 163b is the S-polarized beam, it is reflectedby the PBS 166 and is incident onto the collimate lens 162. The lightbeam 163b, substantially collimated by the collimate lens 162, isincident on the half mirror 164. Then, the component of the light beam163b, reflected by the half mirror 164, is incident on an objective lens167. The objective lens 167 converges the light beam into an imagingpoint p' on the recording face of the CD 168b. Thus, a beam spot 169a isformed on the recording face of the CD 168b.

Thereafter, a light beam 170b, which is the light beam reflected by theoptical disk 169a, repasses through the objective lens 167 and isincident on the half mirror 164. The component transmitting through thehalf mirror 164 pass through the cylindrical lens 172 and the focusinglens 171 in this order, to be incident onto the PSS 174. Since being anS-polarized beam, the light beam 170b is reflected by the PBS 174, andis incident onto a PD 173b for the CD 168b. The PD 173b is configured soas to detect the focus control signal and the tracking control signal bythe astigmatism method and the push-pull method respectively, as well asthe reproduction signal.

Also in the configuration shown in FIG. 6, each of the opticalcomponents of the optical system is designed in accordance with the basematerial thickness and the available wavelength of the thin optical disk168a. Hence, in Example 2, the cover glass 175 for correcting theoptical path length is provided on the optical path between the LD 161bfor the CD 168b and the PBS 166, and thereby the optical path lengthbetween the LD 161b for the CD 168b and the PBS 166 is different fromthe optical path length between the LD 161a for the thin optical disk168a and the PBS 166. The optical path lengths are determined in such away as discussed above with reference to FIGS. 3A and 3B. In this way,it becomes possible to compensate for the wavefront aberration whichoccurs when the light beam 163b of a wavelength suitable for aconventional optical disk, i.e., 780 nm, is focused on the CD 168b byusing the thus designed optical components. As a result, the degree inwhich the light beam 163b is converged on the recording face of the CD168b can be improved so as to be sufficient for reproducing data fromthe CD 168b.

EXAMPLE 3

Now, Example 3 of the present invention is described with reference toFIG. 7. In Example 3, similar to the above-mentioned Example 2, the basematerial thickness of the first optical disk 188a is different from thatof the second optical disk 188b. The available wavelengths of the firstoptical disk 188a and the second optical disk 188b may be the same ordifferent. Similar to the optical heads shown in FIGS. 4 through 6, anoptical head shown in FIG. 7 includes an LD 181a for the thin opticaldisk 188a and an LD 181b for the conventional optical disk 188b, i.e.,an LD which emits a light beam having a wavelength of 780 nm. In thisexample, the conventional optical disk 188b is a CD.

First, the case where a set optical disk is the thin optical disk 188awill be described hereinafter. A light beam 183a output from the LD 181afor the thin optical disk 188a is reflected by a first face of a halfmirror 188, and is incident onto a collimate lens 182. At this time, theLD 181a has output an S-polarized beam as the light beam 183a. Aftercollimated by the collimate lens 182, the light beam 183a is convergedinto an imaging point p on the recording face of a thin optical disk188a. Thus, a beam spot 189a is formed on the recording face of the thinoptical disk 188a.

Thereafter, a light beam 190a, i.e., the light beam 183a reflected bythe optical disk 188a, repasses through the objective lens 187 and thecollimate lens 182, to be incident on the half mirror 186. The halfmirror 186 has a second face serving as a polarized beam splitter, inaddition to the above-mentioned first face. After passing through thefirst face of the half mirror 186, the reflected light beam 190a isreflected by the second face and is incident onto a PD 193a for the thinoptical disk 188a. The PD 193a is configured so as to detect the focuscontrol signal and the tracking control signal by the astigmatism methodand the push-pull method, respectively, as well as the reproductionsignal.

Next, the case where the set optical disk is the CD 188b will bedescribed. The LD 181b for the CD 188b outputs a linearly polarized beamwhose polarization direction is substantially perpendicular to that ofthe light beam 183a. In other words, the light beam 183b is aP-polarized beam. As shown in FIG. 7, the LD 181b for the CD 188b islocated on the optical axis so as to be closer to the half mirror 186than the LD 181a for the thin optical disk 188a. Furthermore, the LDs181a and 181b are adjacent with each other in he direction perpendicularto the optical axis. The light beam 183b is reflected by the first faceof the half mirror 186 and is incident onto a collimate lens 182. Thelight beam 183b substantially collimated by the collimate lens 182 isconverged into an imaging point p' on the recording face of the CD 188b.Thus, a beam spot 189b is formed on the recording face of the CD 188b.

Following this, a light beam 190b, which is the light beam 190areflected by the optical disk 188b, repasses through the objective lens187 and the collimate lens 182 to be incident onto the half mirror 186.Since the reflected light beam 190b is a P-polarized beam, it passesthrough both the first face end the second face of the half mirror 186to be incident onto a PD 193b for the CD 188b. The PD 193b is configuredso as to detect the focus control signal and the tracking control signalby the astigmatism method and the push-pull method, respectively, aswell as the reproduction signal.

Also in the configuration shown in FIG. 7, the collimate lens 182 andthe objective lens 187 are designed in accordance with the base materialthickness and the available wavelength of the thin optical disk 188a.Hence, in Example 3, by locating the LD 181b for the CD 188b so as to becloser to the half mirror 186 than the LD 181a for the thin optical disk188a, it is arranged that the optical path length between the LD 181bfor the CD 188b and the half mirror 186 and the optical path lengthbetween the LD 181a for the thin optical disk 188a and the half mirror186 are different from each other. The optical path lengths aredetermined in such a way as discussed above with reference to FIGS. 3Aand 3B. This arrangement makes it possible to compensate for thewavefront aberration which occurs when the light beam 183b of awavelength suitable for a conventional optical disk, i.e., 780 nm, isfocused on the CD 188b. As a result, the degree in which the light beam183 is converged on the recording face of the CD 188b can be improved toan extent sufficient for reproducing data from the CD 188b.

EXAMPLE 4

Now, Example 4 of the present invention is described with reference toFIGS. 8A and 8B. Example 4, the first optical disk 8a and the secondoptical disk 8b are different both in the base material thickness andthe available wavelength. Similar to the optical heads shown in FIGS. 3through 6, an optical head shown in FIG. 8A and 8B includes an LD 1a forthe first optical disk 8a and an LD 1b for the second optical disk 8b.In this example, the first optical disk 8a is an optical disk whose basematerial is 0.6 mm thick and whose available wavelength is 635 nm, whilethe second optical disk 8b is a conventional optical disk whose basematerial is 1.2 mm thick and whose available wavelength is 780 nm. Inaddition, the recording density of data on the first optical disk 8a ishigher than that on the conventional disk 8b. Hereinafter, an opticaldisk on which the recording density is higher than conventional one issimply referred to as a high-density optical disk.

First, the case where the optical disk inserted is the high-densityoptical disk 8a will be described hereinafter. A light beam 3a outputfrom the LD 1a for the high-density optical disk 8a is incident onto afirst wavelength polarization filter 4a. Herein, the LD 1a outputs aP-polarized beam as the light beam 3a. The first wavelength polarizationfilter 4a is used for combining the optical path of the light beam 3aand that of a light beam 3b from the LD 1b for the optical disk 8b asdescribed later, and has characteristics as shown in FIG. 9A. Therefore,the light beam 3a transmits through the wavelength polarization filter4a and then is incident onto a collimate lens 2. The light beam 3acollimated by the collimate lens 2 is incident onto a second wavelengthpolarization filter 4a'. The second wavelength polarization filter 4a'also has characteristics as shown in FIG. 9A, and is arranged so that itis spatially twisted at 90° with respect to the first wavelengthpolarization filter 4a. Because of this, the light beam 3a is incidentonto a second wavelength polarization filter 4a', as an S-polarizedbeam. Thus, the light beam 3a is reflected by this filter 4a' and isincident onto a wave plate 25. The wave plate 25 is designed so that aphase difference of π/2 arises with respect to the light beam having awavelength of 635 nm. Thus, the light beam 3a is converted into acircularly polarized beam by passing through the wave plate 25. Thecircularly polarized light is converged into an imaging point p on therecording face of the high-density optical disk 8a by an objective lens7. Thus, a beam spot is formed on the recording face of the high-densityoptical disk 8a whose base material is 0.6 mm thick.

Thereafter, a light beam 10a, which is the light beam 3a reflected bythe optical disk 8a, repasses through the objective lens 7 and the waveplate 25 in this order, to be incident on the second wavelengthpolarization filter 4a'. The light beam 10a transmits through the secondwavelength polarization filter 4a', since it has been converted into aP-polarized beam by the function of the wave plate 25. Then, the lightbeam 10a passes through a detection lens 11 and is incident on a PD 13afor the first optical disk 8a. The PD 13a detects the focus controlsignal and the tracking control signal by the astigmatism method and thepush-pull method, respectively, as well as the reproduction signal.

Next, the case where the inserted optical disk is the conventionaloptical disk 8b such as a CD, whose base material is 1.2 mm thick, willbe described. The LD 1b for the optical disk 8b outputs a light beam 3b.The optical head of Example 4 provides a laser diode-photodetectorintegrated module 14, in which the LD 1b, a PD 13b and a hologram 17 areintegrated as one unit. The configuration of this LD-PD integratedmodule is shown in FIG. 15, and will be described later. The hologram 17is used for splitting the light beam reflected by the optical disk 8binto a plurality of beams and spatially changing these beams. The thusarranged module 14 has an advantage in that it can be installed on abase face of the optical head only by adjusting the rotation ofsub-beams for the detection of the tracking control signal. In somecases, no adjustment is required. This is because the relativepositional relationship between the PD 13b and the hologram 17 isadjusted in the assembly process of the LD-PD integrated module 14. Inaddition, though the hologram 17 of Example 4 is provided for splittingthe reflected light beam into a plurality of beams, it may be replacedwith a prism.

As shown in FIG. 8B, passing through an aperture 6, the light beam 3boutput from the LD 1b of the LD-PD module 14 is incident onto the firstwavelength polarization filter 4a. The aperture 6 limits the beam radiusof the light beam 3b so as to form a beam spot having the optimum radiusfor reproducing data from the conventional optical disk 8b whose basematerial is 1.2 mm thick. Since the first wavelength polarization filter4a has transmittance-wavelength characteristics as shown in FIG. 9A, thelight beam 3b is reflected by the first wavelength polarization filter4a regardless of its polarization, and is incident on the collimate lens2. The collimate lens 2 has been designed in accordance with the basematerial thickness and the available wavelength of the above-mentionedhigh-density optical disk 8a. Accordingly, the light beam 3b passedthrough the collimate lens 2 does not become a completely collimatedbeam but a beam a little more scattered than the shove-mentionedcollimated light beam 3a. In succession, the light beam 3b is incidentonto the second wavelength polarization filter 4a' and is reflected atalmost 100% irrespective of its polarization. The light beam 3breflected by the second wavelength polarization filter 4a' passesthrough the wave plate 25 and is converged into an imaging point p' onthe recording face of the optical disk 8b by the objective lens 7. Thus,a beam spot is formed on the recording face of the optical disk 8b whosebase material is 1.2 mm thick.

Thereafter, a light beam 10b, which is the light beam 3b reflected bythe optical disk 8b, repasses through the objective lens 7 end the waveplate to be incident on the second wavelength polarization filter 4a'.The polarization of this light beam 10b has been changed due to thefunction of the wave plate 25. However, since the wavelength of thelight beam 10b is 780 nm, it is reflected at almost 100% by the secondfilter 4a' irrespective of its polarization. Thereafter, the light beam10b passes through the collimate lens 2, and is reflected at almost 100%also by the first wavelength polarization filter 4a. The reflected beamis incident onto the LD-PD integrated module 14. The incident light beam10b is diffracted by the hologram 17 formed on the front face of themodule 14 to be incident onto the PD 13b, which is configured so as todetect the focus control signal by the spot size detection (SSD) methodand the tracking control signal by the three-beam method. By usingtracking signal, a control for making the beam spot on the recordingface of the optical disk 85 follow the reading track is performed.

In Example 4, the collimate lens 2, the objective lens 7 and the likehave been designed in accordance with the thickness of the base material(0.6 mm) and the available wavelength (635 nm) of the thin high-densityoptical disk 8a. As a result, the wavefront aberration arises when thelight beam 3b having a wavelength of 780 nm is converged, by the thusdesigned optical system, on the recording face of the optical disk 8bwhose base material is 1.2 mm thick. For sufficiently reducing thiswavefront aberration, the distance between the LD 1b and the collimatelens 2 is set so as to be different from that between the LD 1a and thecollimate lens 2. Specifically, the optical path lengths are determinedas described above with reference to FIG. 3A.

FIG. 10 shows a system block diagram of the optical datarecording/reproducing apparatus including the optical head of Example 4.When an optical disk is inserted into the apparatus, based on the shapeof a cartridge of the optical disk or the like, a disk discriminator 330judges whether it is the thin high-density optical disk 8a whose basematerial is 0.6 mm thick or the conventional optical disk 8b whose basematerial is 1.2 mm thick. In the case where the optical disk is judgedto be the high-density optical disk 8a whose base material is 0.6 mmthick, an LD drive circuit 320 supplies a current to the LD 1a, so thatthe light beam 3a having a wavelength of 635 nm is output. The lightbeam 3a reflected by the optical disk 8a is incident onto the PD 13a.The control signals and the reproduction signal are obtained based onthe reflected light beam. Meanwhile, in the case where the optical diskis judged to be the optical disk 8b whose base material is 1.2 mm thick,the LD 1b is driven by a current from the LD drive circuit 320, so thatthe light beam 3b having a wavelength of 780 nm is output. The lightbeam 3b reflected by the optical disk 8b is incident onto the PD 13b,and the control signals and the reproduction signal are obtained byusing the light beam incident onto the PD 13b.

In the configuration as shown in FIGS. 8A and 8B, the wavelengthpolarization filter 4a having characteristics as shown in FIG. 9A isemployed. Hence, the wave plate 25 only functions as an isolator solelyfor the light beam 3a of a wavelength of 635 nm, while there is nonecessity for providing an isolator for the light beam 3b of awavelength of 780 nm. Thus, this system can be fabricated usinginexpensive components. In addition, since the first and secondwavelength polarization filters 4a and 4a' are of the same design, theoptical head can be fabricated at a low cost. Furthermore, it ispossible to minimize the number of reflecting planes by which the lightbeam 3a of a wavelength of 635 nm is reflected on the optical path fromthe LD 1a to the imaging point p on the recording face of thehigh-density optical disk 8a, resulting in an improved accuracy of thewavefront aberration at the imaging point p. Thus, good reproductioncharacteristics can be obtained.

In this Example 4, in order to combine the optical path of the lightbeam 3a from the LD 1a and that of the light beam 3b from the LD 1b, thefirst wavelength polarization filter 4a having the characteristics shownin FIG. 9A is employed. However, the first wavelength polarizationfilter 4a can be replaced with a known polarized beam splitter for alight beam of a wavelength of 635 nm. In this case, the fabricationcosts can be further reduced.

EXAMPLE 5

Now, Example 5 of the present invention is described with reference toFIGS. 11A and 11B. Also in Example 5, the first and the second opticaldisks 8a and 8b are different both in the thickness of the base materialand in the available wavelength. The optical head of Example 5 includesan LD 1a for the first optical disk 8a and an LD 1b for the secondoptical disk 8b. In this example, the first optical disk 8a is ahigh-density optical disk whose base material is 0.5 mm thick and whoseavailable wavelength is 535 nm, while the second optical disk 8b is anoptical disk whose base material is 1.2 mm thick and whose availablewavelength is 780 nm.

First, the case where the inserted optical disk is the high-densityoptical disk 8a will be described. The LD 1a of an oscillationwavelength of 635 nm outputs a P-polarized beam as the light beam 3a.The light beam 3a transmits through a first wavelength polarizationfilter 4a having characteristics as shown in FIG. 9A and a secondwavelength polarization filter 4b having characteristics as shown AnFIG. 9B, to be incident onto a collimate lens 2. The light beam 3asubstantially collimated by the collimate lens 2 is reflected by amirror 21 and incident onto a wave plate 5. Herein, the wave plate 5 isset so as to generate a phase difference of π/2 with respect to a lightbeam of a wavelength of 635 nm and a phase difference of π with respectto a light beam of a wavelength of 780 nm. Therefore, the light beam 3ais converted into a circularly polarized beam by passing through thewave plate 5. The circularly polarized beam 3a is incident onto anobjective lens 7. The objective lens 7 converts the light beam 3a intoan imaging point p on the recording face of the high-density opticaldisk 8a. Thus, a beam spot is formed on the recording face of thehigh-density optical disk 8a.

Thereafter, a light beam 10a, i.e., the light beam 3a reflected by theoptical disk 8a, repasses through the objective lens 7, the wave plate5, the mirror 21 end the collimate lens 2 in this order, so as to beincident on the second wavelength polarization filter 4b. Since thesecond wavelength polarization filter 4b has characteristics as shown inFIG. 9B, the light beam 10a transmits through the wavelengthpolarization filter 4b irrespective of its polarization, and then almost100% of the transmitted light beam 10a is reflected by the wavelengthpolarization filter 4a. The reflected light beam 10a passes through adetection lens 31 and is incident onto a PD 13a. The PD 13a detects thefocus control signal and the tracking control signal by the astigmatismmethod and the push-pull method, respectively, as well as thereproduction signal.

Next, the case where the inserted optical disk is the optical disk 8bsuch as a CD, whose base material is 1.2 mm thick, will be described.The LD 1b of an oscillation wavelength of 780 nm outputs a light beam3b. The optical head of Example 5 provides the LD-PD integrated module14 having the configuration shown in FIGS. 15 and 16. The detailedconfiguration of the LD-PD integrated module 14 will be described later.The 780 nm LD 1b provided in the LD-PD integrated module 14 outputs alinearly polarized beam whose polarization direction is perpendicular tothat of the light beam 3a output from the LD 1a. That is, the light beam3b output from the LD 1b is an S-polarized beam.

As shown in FIG. 11B, the light beam 3b output from the 780 nm LD 1b ofthe LD-PD integrated module 14 passes through the aperture 6 to beincident onto the first wavelength polarization filter 4b. The aperture6 adjusts a beam radius of the light beam 3b so that a beam spot havingan optimum radius for reproducing data from the optical disk 8b isformed on the recording face of the optical disk 8b whose base materialas 1.2 mm thick. The light beam 3b is reflected by the second wavelengthpolarization filter 4b, since the second wavelength polarization filter4b has transmittance-wavelength characteristics as shown in FIG. 9B. Thelight beam 3b is then incident on the collimate lens 2. This collimatelens 2 has been designed in accordance with the thickness of the basematerial of the above-mentioned disk 8a and the wavelength of the lightbeam 3a. As a result, the light beam 3b passed through the collimatelens 2 becomes not a completely collimated beam but a beam a little morescattered than the above-mentioned collimated light beam 3a. Thescattered beam 3b is reflected by a mirror 21, and thereafter isincident onto the wave plate 5. When the light beam 3b passes throughthe wave plate 5, the wave plate 5 gives the phase difference of π tothe light beam 3b of a wavelength of 780 nm as described above, so as torotate the polarization direction of the light beam 3b by 90°. Insuccession, the light beam 3b is incident onto the objective lens 7 tobe converged into an imaging point p' on the recording face of theoptical disk 8b. Thus, a beam spot is formed on the recording face ofthe optical disk 8b whose base material is 1.2 mm thick.

Thereafter, a light beam 10b, i.e., the light beam 3b reflected by theoptical disk 8b, repasses through the objective lens 7, the wave plate5, the mirror 21 and the collimate lens 2 in this order, to be incidenton the second wavelength polarization filter 4b. At this time, the lightbeam 10b has become an S-polarized beam, with its polarization directionrotated over 90° by the function of the wave plate 5. Because of this,the light beam 10b is reflected at almost 100% by the second wavelengthpolarization filter 4b, and the reflected beam is incident onto theLD-PD integrated module 14. The light beam 10b incident onto the module14 is diffracted by a hologram 17 formed on the front face of the module14, and the diffracted beams are incident onto the PD 13b. Similarly toExample 4, the PD 13b detects the focus control signal end the trackingcontrol signal as well as the reproduction signal.

In Example 5, in order to make the optical head thinner and morecompact, the mirror 21 is used for bending the optical paths. Thus,whether the mirror 21 exists or not is irrespective of the operation ofthe optical head. Accordingly, the light beam output from the collimatelens 2 may be incident directly onto the wave plate 5, without beingreflected by the mirror 21.

Also in Example 5, the collimate lens 2, the objective lens 7 and thelike are designed in accordance with the base material thickness (0.6mm) and the available wavelength (635 nm) of the optical disk 8a. As aresult, in order to reduce a wavefront aberration generated when theoptical beam 3b is converged onto the optical disk 8b whose basematerial is 1.2 mm thick and available wavelength is 780 nm, the opticalpath length between the LD 1b and the collimate lens 2 is set so as tobe different from the optical path length between the LD 1a and thecollimate lens 2. The optical path length between the LD 1b and thecollimate lens 2 is determined as discussed above with reference to FIG.3A.

Moreover, Example 5 makes it possible to minimize the number of planesby which the light beam 3a of a wavelength of 635 nm is reflected on theoptical path from the LD 1a to the imaging point p on the recording faceof the high-density optical disk 8a whose base material is 0.6 mm thick.As a result, an accuracy of the wavefront aberration at the imagingpoint p is improved, which assures good reproduction characteristics.

EXAMPLE 6

Now, Example 6 of the present invention is described with reference toFIGS. 12A and 12B. Also in Example 6, optical disks 8a and 8b aredifferent both in the thickness of the base material and in theavailable wavelength. The base material thickness and availablewavelength of the optical disk 8a, those of the optical disk 8b, and theoscillation wavelengths of an LD 1b for the optical disk 8b and an LD 1bfor the optical head 8b are the same as described in Example 5.

FIG. 12A shows the case where the high-density optical disk 8a whosebase material is 0.6 mm thick is inserted in the optical datarecording/reproducing apparatus using the optical head of Example 6, andFIG. 12B shows the case where the optical disk 8b whose base material is1.2 mm thick is inserted therein. In Example 6, the wave plate 25 isused in place of the wave plate 5 of Example 5. Similarly to Example 4,the wave plate 25 is set so as to provide a phase difference of π/2 witha light beam of a wavelength of 635 nm, and is disposed between thefirst wavelength polarization filter 4a and the second wavelengthpolarization filter 4b instead of being on the optical path between amirror 21 and an objective lens 7. Consequently, the wave plate 25changes only the polarization direction of a light beam 3a output fromthe LD 1a of an oscillation wavelength of 635 nm, without affecting thelight beam 3b output from the LD-PD integrated module 14. In addition,in Example 6, a movable plate 27 having an aperture is mounted on anactuator 26 for moving the objective lens 7 at the side facing themirror 21. The movable plate 27 is retracted from the optical path whenthe recording/reproducing operation of the high-density optical disk 8ais performed, and is moved so as to be on the optical path when therecording/reproducing operation of the optical disk 8b whose basematerial is 1.2 mm thick is performed. That is, the entire aperture ofthe objective lens 7 is used for the high-density optical disk 8a, whileat the time of performing the recording/reproducing operation of theoptical disk 8b whose base material is 1.2 mm thick the beam radius ofthe light beam 3b is adjusted so that a beam spot having the radiusoptimum for the reproducing operation of the optical disk 8b is formed.Except for the differences in the optical configuration as describedabove, the optical configuration of the optical head of Example 6 is thesame as that of Example 5.

In Example 6, the characteristics of the wave plate 25 are free fromrestrictions with respect to the light beam of a wavelength of 780 nm,as long as it functions as a normal quarter-wave plate solely for thelight beam of e wavelength of 635 nm. Thus, an inexpensive opticalcomponent can be used as the wave plate 25, which allows the opticalhead to be fabricated at a lower cost.

Furthermore, since the movable plate 27 having the aperture is disposedon the optical path, when the objective lens actuator 26 follows themovement of track due to the eccentricity of the optical disk, the lightamount of the light beam converged on the optical disk is reduced or theaberration on the optical disk is increased. However, in Example 6,since the movable plate 27 having the aperture is integrally provided inthe objective lens actuator the aperture moves along with the movementof the objective lens actuator 26, whereby the reduction of the lightamount of the converged beam 3b and the increase of the aberration onthe optical disk 8b can be lessened.

EXAMPLE 7

Now, Example 7 of the present invention is described with reference toFIGS. 13A end 13B. Also in Example 7, the first optical disk 8a and thesecond optical disk 8b are different both in the thickness of the basematerial and in the available wavelength, and an LD 1a for the firstoptical disk 8a and an LD 1b for the second optical disk 8b are providedin the optical head. The first optical disk 8a is a high-density diskwhose base material thickness and the available wavelength of the highdensity thin-shaped optical disk 8a are 0.6 mm and 635 nm, respectively.The base material thickness and the available wavelength of the opticaldisk 8b are 1.2 mm and 780 nm.

First, the case where an optical disk which is to be recorded orreproduced is the thin high-density optical disk 8a will be described. Alight beam 3a output from the LD 1a of an oscillation wavelength of 635nm, is incident onto the first wavelength polarization filter 44a.Herein, the LD 1a outputs an S-polarized beam as the light beam 3a. Thewavelength polarization filter 44a is a filter having characteristics asshown in FIG. 9A end has a plate shape in which the two main surfacesare substantially parallel to each other. Thus, the light beam 3a isreflected by one of the two main surfaces of the first wavelengthpolarization filter 44a, and then is incident onto the second wavelengthpolarization filter 4b. Since this filter 4b has characteristics asshown in FIG. 9B, the light beam 3a is transmitted irrespective of itspolarization, and is incident onto a collimate lens 2. Having beencollimated by the collimate lens 2, the light beam 3a is reflected by amirror 21 and is incident onto the wave plate 5. Similar to theabove-mentioned Example 5, the wave plate 5 is set so as to provide aphase difference of π/2 with a light beam of a wavelength of 635 nm andthat of π with a light beam of a wavelength of 780 nm. Therefore, thelight beam 3a is converted into a circularly polarized beam by passingthrough the wave plate 5, and thereafter is incident onto an objectivelens 7. The objective lens 7 converges the light beam 3a into an imagingpoint p on the recording face of the high-density optical disk 8a. Thus,a beam spot is formed on the recording face of the optical disk 8a.

Thereafter, a light beam 10a, which is the light beam 3a reflected bythe optical disk 8a repasses the objective lens 7, the wave place 5, themirror 21 and the collimate lens 2 in this order so as to be incidentonto the second wavelength polarization filter 4b. The light beam 10atransmits the second wavelength polarization filter 4b irrespective ofits polarization, and is incident onto the first wavelength polarizationfilter 44a. Since the light beam 10a has been converted into aP-polarized beam by passing through the wave plate 5, the light beam 10atransmits through the first wavelength polarization filter 44a, passesthrough a detection lens 51, and is incident onto a PD 13a for theoptical disk 8a. The PD 13a is configured so as to detect the focuscontrol signal by the astigmatism method, in which an astigmatism causedby the light beam 10a passing through the parallel two main surfaces ofthe first wavelength polarization filter 44a is detected, and thetracking signal by the push-pull method.

Next, the case where the optical disk to be recorded or reproduced isthe optical disk 8b such as a CD, whose base material is 1.2 mm thick,will be described. The LD 1b of an oscillation wavelength of 780 nmoutputs a light beam 3b. In Example 7, the LD 1b is disposed so as tooutput a linearly polarized beam whose polarization direction isperpendicular to that of the light beam 3a output by the LD 1a for thehigh-density optical disk. That is, the LD 1b emits a P-polarized beamas the light beam 3b. Similar to Examples 4 through 6, the LD 1b isprovided in the LD-PD integrated module 14. The configuration of theLD-PD integrated module 14 is shown in FIGS. 15 and 16 and will bedescribed later. As becomes apparent by comparing FIG. 13B with FIG.11B, the optical configuration of Example 7 in the case of performingthe recording/reproducing operation of the optical disk 8b whose basematerial is 1.2 mm thick is the same as the optical configuration ofExample 5.

Also in Example 7, the collimate lens 2, the objective lens 7 and thelike are designed in accordance with the base material thickness (0.6mm) and the available wavelength (635 nm) of the optical disk 8a.Because of this, the optical path length between the LD 1b for theoptical disk 8b and the collimate lens 2 is set so as to be differentfrom the optical path length between the LD 1a for the optical disk 8aand the collimate lens 2, as described above with reference to FIG. 3A.As a result, also in Example 7, the wavefront aberration arising whenthe optical beam 3b is converged onto the optical disk 8b can be reducedto such an extent as negligible in performing the recording/reproducingoperation of the optical disk 8b.

Moreover, in Example 7, a filter having a plate shape in which two mainsurfaces are parallel with each other is used as the first wavelengthpolarization filter 44a for separating the optical path of the opticalbeam 3a output from the LD 1a and that of the reflected beam 10a fromeach other. Since the focus control signal can be detected by using theastigmatism generated by means of this plate-shape filter 44a, there isno necessity of especially providing optical components for generatingthe astigmatism. This makes it possible to reduce the number of opticalcomponents used in the optical head, which assures an inexpensiveoptical head.

In Example 7, a filter having characteristics as shown in FIG. 9a isused as the first wavelength polarization filter 44a. This filter 44amay be replaced with a standard-type polarized beam splitter (PBS) for alight beam of a wavelength of 635 nm, whereby the fabrication cost ofthe optical head can be further reduced.

The optical head of Example 7 is preferably designed so that theincidence angle of the light beam 3a with respect to one of the two mainsurfaces of the first wavelength polarization filter 44a is 45° or more.

EXAMPLE 8

Now, Example 8 of the present invention is described with reference toFIGS. 14A and 14B. Also in Example 8, the first optical disk 8a and thesecond optical disk 8b are different both in the thickness of the basematerial and in the available wavelength, and an LD 1a for the firstoptical disk 8a and an LD 1b for the second optical disk 8b are providedin the optical head. However, unlike the above discussed Examples 4through 6, each of the LDs 1a and 1b is provided in the LD-PD integratedmodule. Both of the LD-PD integrated modules have the same configurationas shown in FIG. 15. In Example 8, the first optical disk 8a is ahigh-density optical disk 8a whose base material is 0.6 mm thick andwhose available wavelength is 635 nm, and the second optical disk 8b isan optical disk whose base material is 1.2 mm and whose availablewavelength is 780 nm. The oscillation wavelengths of the LDs 1a and 1bare 635 nm and 780 nm, respectively.

First, the case where an optical disk to be recorded or reproduced isthe high-density optical disk 8a will be described. A light beam 63aoutput from the LD 1a, provided in a first LD-PD integrated module 74,is incident onto a wavelength polarization filter 4a havingcharacteristics as shown in FIG. 9a. Since the LD 1a outputs aP-polarized beam as the light beam 63a, the light beam 63a transmitsthrough the wavelength polarization filter 4a. By means of an objectivelens 67, the transmitted light beam 63a is converged into an imagingpoint p on the recording face of the high-density optical disk 8a whosebase material is 0.6 mm thick. Thus, a beam spot is formed on therecording face of the high-density optical disk 8a.

Thereafter, a light beam 70a, which is the light beam 63a reflected bythe high-density optical disk 8a, repasses through the objective lens 67and the wavelength polarization plate 4a in this order, to be incidenton the first LD-PD integrated module 74. The incident light beam 70a isdiffracted by a hologram 77 formed on the front face of the LD-PDintegrated module 74. The diffracted light beams are incident onto a PD73. The PD 73 is configured so as to detect the focus control signal andthe tracking control signal by the SSD method and the three-beam method,respectively, as well as the reproduction signal.

Next, the case where the optical disk to be recorded or reproduced isthe optical disk 8b such as a CD, whose base material is 1.2 mm thick,will be described. The LD 1b of an oscillation wavelength of 780 nm,provided in a second LD-PD integrated module 61, outputs a light beam63b. The LD 1b is disposed so as to output a linearly polarized beamwhose polarization direction is perpendicular to that of the light beam63a output from the LD 1a for the optical disk 8a. That is, the LD 1boutputs an S-polarized beam.

FIG. 15 shows the arrangement of optical components included in each ofthe LD-PD integrated modules in an enlarged form. Herein, theconfiguration of the second LD-PD integrated module 61 is described forexample. In FIG. 15, the light beam 63b output from the LD 1b isreflected by a mirror 82 and is incident onto a ring-shaped grating 83,wherein the light beam 63a is divided into a main beam (a 0th orderbeam) and two sub-beams (±1st order beams) to be used for detecting thetracking control signal. The shape of the ring-shaped grating 83 isshown in FIG. 16. In designing the ring-shaped grating 83, the depth Dof grooves is determined so that where n stands for the reflective indexof the grating 83, (n-1) becomes 2/N times the wavelength of the lightbeam 63b. The width L1 of a convex portion and the width L2 of thegroove have a ratio of 1:1. In addition, the diffraction efficiency ofthe 0th beam of the ring-shaped grating 83 is theoretically 0%. That is,the ring-shaped grating 83 limits the radius of the main beam.Accordingly, the light beam 63 is, with its beam radius having beennarrowed by the ring-shaped grating 83, converged onto the optical disk8b whose base material is 1.2 mm thick so as to form a beam spot havingan optimum spot radius for recording/reproducing data on and from theoptical disk 8b.

In FIG. 14B, the light beam 63b output from the second LD-PD integratedmodule 61 is reflected by the wavelength polarization filter 4a to beincident onto the objective lens 67. The light beam 63b is converged bythe objective lens 67 into an imaging point p' on the recording face ofthe optical disk 8b whose base material is 1.2 mm thick, and thus a beamspot is formed on the recording face of the optical disk 8b. Thereafter,a light beam 70b, i.e., the light beam 63b reflected by the optical disk8b, repasses through the objective lens 67, and is reflected by thewavelength polarization filter 4a to be incident on the second LD-PDintegrated module 61. The incident light beam 70b is diffracted by ahologram 17 formed on the front face of the LD-PD integrated module 61,and the diffracted light beams are incident onto a PD 13b. The hologram17 is designed so that the diffracted light beams cannot be incident onthe ring-shaped grating 83. The PD 13b detects the focus control signaland the tracking control signal by the SSD method and the three-beammethod, respectively, as well as the reproduction signal.

Two LD-PD integrated modules are provided in the optical head of Example8. So, a compact, inexpensive and simply configured optical head isrealized, because the number of optical components can be reduced. Inaddition, since the beam radius of the light beam 63b in therecording/reproducing operation of the optical disk 8b whose basematerial is 1.2 mm thick is limited by the ring-shaped grating 83 forgenerating the sub-beams as shown in FIG. 15, the eclipse of thesub-beams at the lens aperture can be reduced. As a result, the lightbeam 63a output from the LD 1b can be used more efficiently.

In Example 8, only the ring-shaped grating has the function of adjustingthe beam radius of the light beam emitted from the LD. However, theoptical head may further include another optical component having theabove-described function such as the aperture as in Examples 4 to 7. Inthis case, the aperture can be disposed anywhere on the optical pathfrom the LD to the objective lens. For example, the movable plate 27 asshown in FIG. 12B having an aperture can be attached to the actuator 26for moving the objective lens 7. The aperture 6 can be disposed betweenthe LD and the wavelength polarizing filter. In addition, in the case ofproviding an optical component having a function of adjusting the beamradius, other than the ring-shaped grating in the LD-PD integratedmodule, the inner radius of the ring-shaped grating may be smaller thanthe radius of the optical component for adjusting the beam radius.

Furthermore, in the present Example 8, the polarization direction of thelight beam 63b of a wavelength of 635 nm output from the first LD-PDintegrated module 74 is rendered a P-polarized beam. However, by usingthe wavelength polarization filter 4b having characteristics as shown inFIG. 9B in place of the wavelength polarization filter 4a, the firstLD-PD integrated module 74 can be arranged to output an S-polarizedbeam. In this case, the light beam 63b of a wavelength of 780 nm, outputfrom the second LD-PD integrated module 61, becomes such a polarizedbeam that it can be reflected by the wavelength polarization filter 4b,i.e., an S-polarized beam. Thus, by modifying the characteristics of thewavelength polarization filter, the polarization direction of the lightbeam incident onto this filter can be changed. This makes it possible tochange the arrangement of each of the LD-PD integrated modules. Inaddition, by adding a rising mirror or the like to the opticalconfiguration as shown in FIGS. 14A and 14B, the optical head can berendered thinner.

EXAMPLE 9

Example 9 of the present invention is described with reference to FIGS.17A and 17B. In Example 9, the first optical disk 108a and the secondoptical disk 108b have the same base material thickness, while beingdifferent in the available wavelength. In Example 9, the base materialthickness of the optical disks 108a and 108b is 1.2 mm, and theavailable wavelengths of the optical disks 108a and 108b are 635 nm and780 nm, respectively.

The first optical disk 108a is a high-density disk. First, withreference to FIG. 17A, the case where an optical disk to be recorded orreproduced is the high-density optical disk 108a will be described. Alight beam 103a output from an LD 1a of an oscillation wavelength of 635nm, is incident onto the first wavelength polarization filter 4a havingcharacteristics as shown in FIG. 9A. Since the LD 1a is arranged so asto output a P-polarized beam as the light beam 103a, the light beam 103apasses through the first wavelength polarization filter 4a, and then issubstantially collimated by a collimate lens 102. Thereafter, thecollimated light beam is incident onto a second wavelength polarizationfilter 4a'. This second wavelength polarization filter 4a' also has thecharacteristics as shown in FIG. 9A, but is disposed being spatiallytwisted at 90° with respect to the first wavelength polarization filter4a. Because of this, the light beam 103a is incident onto the secondwavelength polarization filter 4a as an S-polarized beam, and isreflected thereby. In succession, the light beam 103a is incident ontothe wave plate 25. Similarly to Example 1, the wave plate 25 is designedso as to provide a phase difference of π/2 with a light beam of awavelength of 635 nm. Therefore, the light beam 103a is converted froman S-polarized beam into a circularly polarized beam, by passing throughthe wave plate 25. An objective lens 107 converts the circularlypolarized beam 103a into an imaging point p on the recording face of thehigh-density optical disk 108a. Thus, a beam spot is formed on therecording face of the high-density optical disk 108a.

The light beam 103a is reflected by the high-density optical disk 108ato be incident onto the objective lens 107 again, as a reflected beam110a. In succession, the light beam 110a incident onto the wave plate 25is converted from the circularly polarized beam to a P-polarized beam,and thereafter is incident onto the second wavelength polarizationfilter 4a'. Since the second wavelength polarization filter 4a' has thecharacteristics as shown in FIG. 9A, the light beam 110a passes throughthe filter 4a' without being affected thereby. Then, via e detectionlens 111, the light beam 110a is incident onto a PD 13 for the firstoptical disk 8a. On the basis of the incident light beam 110a, the PD 13detects the focus control signal and the tracking control signal as wellas the reproduction signal. In Example 9, the focus signal is detectedby the astigmatism method, while the tracking control signal is detectedby the push-pull method.

FIG. 17B shows the optical path in the case where the optical disk to berecorded or reproduced is the optical disk 108b whose availablewavelength is 780 nm. In this case, the optical configuration and thedetailed configuration of the LD-PD integrated module 14 are the same asdiscussed above in Example 4.

Also in the present Example 9, the collimate lens 102, the objectivelens 107 and the like are designed in accordance with the base materialthickness (1.2 mm) and the available wavelength (635 nm) of thehigh-density optical disk 108a. For this reason, the LD-PD integratedmodule 14 is disposed at a position such that the optical path lengthbetween the LD 1b and the collimate lens 102 is different from theoptical path length between the LD 1a and the collimate lens 102. Morespecifically, the optical path length between the LD 1b and thecollimate lens 102 is determined as described above referring to FIG.3B. For example, it is assumed that the focal length of the collimatelens 102 and that of the objective lens are 3.7 mm and 22.5 mm,respectively, and the converging optical system is designed so that thelight beam 103a from the LD 1a is converged on the optical disk 8a whoseavailable wavelength is 635 nm in such a way that the wavefrontaberration becomes 10 mλ (rms) or less. In this case, as is apparentfrom FIG. 3B, it is when the optical path length between the LD 1b andthe collimate lens 102 is about 21.8 mm that the wavefront aberrationwhen the light beam 103b is converged on the optical disk 108b isminimized. In this way, by adjusting the optical path length between theLD 1b for the optical disk 108b and the collimate lens 102, even whenusing the optical system designed in accordance with the base materialthickness and the available wavelength of the optical disk 108a, thewavefront aberration caused by converging the light beam 103b on theoptical disk 108b can be reduced to such a low level as to be negligiblein the recording/reproducing operation of the optical disk 108b.

The configuration of this Example 9 employs the first wavelengthpolarization filter 4a having characteristics as shown in FIG. 9A.Hence, the wave plate 25 only functions as an isolator solely for thelight beam 103a of a wavelength of 635 nm, while there is no necessityof providing an isolator for the light beam 103b of a wavelength of 780nm. Thus, this system can be fabricated using inexpensive components. Inaddition, since the first and second wavelength polarization filters 4aand 4a' are of the same design, the optical head can be fabricated at alow cost. Furthermore, it is possible to minimize the number of planesby which the light beam 103a of a wavelength of 635 nm is reflected onthe optical path from the LD 1a to the imaging point p on the recordingface of the high-density optical disk 108a. Accordingly, the wavefrontaberration at the imaging point p can be obtained more accurately. Thus,good reproduction characteristics are realized.

Example 9 employs the first wavelength polarization filter 4a havingcharacteristics as shown in FIG. 9A, in order to combine the opticalpath of the light beam 103a from the LD 1a and that of the light beam103b from the LD 1b. This first wavelength polarization filter 4a can bereplaced with a standard-type polarized beam splitter for a light beamof a wavelength of 635 nm. In this case, the fabrication cost can befurther reduced.

EXAMPLE 10

Example 10 of the present invention is described with reference to FIGS.18A and 18B. In Example 10, the first optical disk 108a and the secondoptical disk 108b have the same base material thickness, while beingdifferent in the available wavelength. This example is described on theassumption that the base material thickness of the optical disks 108aand 108b is 1.2 mm, and the available wavelengths of the optical disks108a and 108b are 635 nm and 780 nm, respectively. Similar to theabove-mentioned Example 9, an optical head of Example 10 includes an LD1a for the first optical disk 108a and an LD 1b for the second opticaldisk 108b. However, unlike Example 9, these LDs 1a and 1b are providedLD-PD integrated modules 135 and 61, respectively.

First, with reference to FIG. 18A, the case where an optical disk to berecorded or reproduced is the high-density optical disk 108a will bedescribed. A light beam 123a output from the LD 1a of an oscillationwavelength of 635 nm is incident onto a first wavelength polarizationfilter 4a having characteristics as shown in FIG. 9A. Since the LD-PDintegrated module 135 is disposed so that a P-polarized beam is outputfrom the LD 1a as the light beam 123a, the light beam 123a passesthrough the first wavelength polarization filter 4a to be incident ontoan objective lens 107. The objective lens 107 converges the transmittedlight beam 123a into an imaging point p on the recording face of thehigh-density optical disk 108a. Thus, a beam spot is formed on therecording face of the high-density optical disk 108a.

The light beam reflected by the high-density optical disk 108a isincident onto the objective lens 107 again, as a light beam 130a. Thelight beam 103a passes through the wavelength polarization filter 4a tobe incident onto the laser-detector integrated module 135. The incidentlight beam 130a is diffracted by a hologram 17 formed on the front faceof the module 135. The diffracted beams are incident onto a PD 73 forthe high-density optical disk 108a. The PD 73 is configured so as todetect a focus control signal by the SSD method and the tracking controlsignal by the three-beam method, respectively, as well as thereproduction signal.

FIG. 18B shows the optical path in the case where the optical disk to berecorded or reproduced is the optical disk 108b whose availablewavelength is 780 nm. As is apparent from FIG. 18B, the configuration ofthe optical head in this case, which is the same as that of theabove-mentioned Example 8, will not described in detail here. It is tobe noted that the LD-PD integrated module 61 is designed so thatpolarization direction of a linearly polarized beam output from the LD1b is perpendicular to that of a linearly polarized beam output from theLD 1a. The detailed configuration of the LD-PD integrated module 61 issimilar to that of Example 8.

Also in the present Example 10, the collimate lens 102, the objectivelens 107 and the like are designed in accordance with the base materialthickness (1.2 mm) and the available wavelength (635 nm) of thehigh-density optical disk 108a. For this reason, the LD-PD integratedmodule 61 is disposed at a position such that the optical path lengthbetween the LD 1b and the collimate lens 102 is different from theoptical path length between the LD 1a and the collimate lens 102. Morespecifically, the optical path length between the LD 1b and thecollimate lens 102 is determined as described above referring to FIG.3B. In this way, by adjusting the optical path length between the LD 1bfor the second optical disk 108b and the collimate lens 102, even whenusing the optical system designed in accordance with the base materialthickness and the available wavelength of the first optical disk 108a,the wavefront aberration caused by converging the light beam 123b on thesecond optical disk 108b can be reduced to such a low level asnegligible in the recording/reproducing operation of the second opticaldisk 108b.

In Example 10, similar to the above-mentioned Example 8, a simpleoptical configuration is realized by using two LD-PD integrated modules.As a result, a compact and inexpensive optical head can be obtained.

Furthermore, the configuration of Example 10 makes it possible toeliminate the reflecting plane by which the light beam 123a of awavelength of 635 nm is reflected on the optical path from the LD 1a tothe imaging point p on the recording face of the high-density opticaldisk 8a whose base material is 1.2 mm thick. As a result, the accuracyof the wavefront aberration at the imaging point p can be improved,which leads to good reproduction characteristics.

Moreover, though the light beam 123a of a wavelength of 635 nm outputfrom the first LD-PD integrated module 135 is rendered a P-polarizedbeam in Example 10, the light beam 123a can be rendered an S-polarizedbeam by using the wavelength polarization filter 4b havingcharacteristics as shown in FIG. 9B in place of the wavelengthpolarization plate 4a. In this case, the light beam 123b of a wavelengthof 780 nm, output from the second LD-PD integrated module 61, becomessuch a polarized beam as can be reflected by the wavelength polarizationfilter 4b, i.e., an S-polarized beam. Thus, by modifying thecharacteristics of the wavelength polarization filter, the polarizationdirection of the light beam incident onto the filter can be changed.This makes it possible to change the arrangement of each of the LD-PDintegrated modules. In addition, by adding a rising mirror or the liketo the optical configuration as shown in FIGS. 18A and 18B, it becomespossible to make the optical head thinner.

In the above-mentioned Examples 4 through 10, the wavelengthpolarization filter 4a or 4b having the characteristics as shown in FIG.9A or 9B is employed. However, a wavelength polarization filter havingcharacteristics as shown in FIG. 20A or 20B may be employed depending onthe application, and thereby the same effects as discussed in connectionwith Examples 4 through 10 can also be obtained.

As described hereinbefore, according to the present invention, oneoptical head includes an LD for each of the first and second opticaldisks that are different in at least one of the base material thicknessand the available wavelength. The LDs are arranged so that the opticalpath length between a converging optical system designed in accordancewith the base material thickness and the available wavelength of thefirst optical disk and the LD for the second optical disk is differentfrom the optical path length between the converging optical system andthe LD for the first optical disk. This makes it possible to perform arecording/reproducing operation for both of the first and second disksby one optical head. Furthermore, each of the LDs has a differentoscillation wavelength or is arranged so as to output a light beam of adifferent polarization direction, which allows the optical path of thelight beam output from one of the LDs to be readily combined with orseparated from that of the other LD.

Additionally, at least one of the LDs respectively provided for each ofthe first and second optical disks may be integrated with aphotodetector so as to form one unit, whereby the configuration of theoptical head can be made more simple.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. An optical head for reproducing data from firstand second optical disks which are different from each other in at leastone of a base material thickness and an available wavelength,comprising:a first light source for emitting a first light beam, thefirst light beam being used for reproducing data from the first opticaldisk; an optical system designed to converge the first light beam ontothe first optical disk in accordance with a base material thickness andan available wavelength of the first optical disk; and a second lightsource for emitting a second light beam, the second light beam beingused for reproducing data from the second optical disk, wherein anoptical path length between the second light source and the opticalsystem is different from an optical path length between the first lightsource and the optical system, the difference between the optical pathlength from the first light source to the optical system and the opticalpath length from the second light source to the optical systemcompensating a wave-front aberration due to the differences in the atleast one of the base material thickness and the available wavelength ofthe first and the second optical disks. and wherein the optical systemconverges the second light beam onto the second optical disk.
 2. Anoptical head according to claim 1, wherein the first optical disk has afirst available wavelength and a first base material thickness, and thesecond optical disk has a second base material thickness, the first basematerial thickness being less than the second base material thickness,and the optical path length between the second light source and theoptical system being less than the optical path length between the firstlight source and the optical system.
 3. An optical head according toclaim 1, wherein the first optical disk has a first available wavelengthand a first base material thickness, and the second optical disk has asecond available wavelength, the first available wavelength beingshorter than the second available wavelength, and the optical pathlength between the second light source and the optical system being lessthan the optical path length between the first light source and theoptical system.
 4. An optical head according to claim 2, wherein thesecond optical disk has a second available wavelength and the firstavailable wavelength is shorter than the second available wavelength. 5.An optical head according to claim 1, wherein the optical path lengthbetween the second light source and the optical system is determined insuch a manner that a wavefront aberration generated when converging thesecond light beam onto the second optical disk becomes minimum.
 6. Anoptical head according to claim 1, further comprising combining meansfor guiding the first and second light beams to the optical system, thecombining means being disposed at a position between the optical systemand the first light source and between the optical system and the secondlight source.
 7. An optical head according to claim 1, furthercomprising first detecting means for detecting the first light beamreflected by the first optical disk.
 8. An optical head according toclaim 7, further comprising second detecting means for detecting thesecond light beam reflected by the second optical disk.
 9. An opticalhead according to claim 8, wherein the first detecting means is aphotodetector provided with a multi-divided detecting face, thephotodetector also being used as the second detecting means.
 10. Anoptical head according to claim 8, further comprising separating meansfor guiding the first light beam reflected by the first optical disk tothe first detecting means and for guiding the second light beamreflected by the second optical disk to the second detecting means. 11.An optical head according to claim 10, wherein the separating means isdisposed at a position between the optical system and the first lightsource and between the optical system and the second light source, andguides the first and second light beams to the optical system.
 12. Anoptical head according to claim 1, further comprising optical pathlength correcting means disposed between the second light source and theoptical system.
 13. An optical head according to claim 8, wherein thefirst light source and the first detecting means are integrally providedas a first unit.
 14. An optical head according to claim 8, wherein thesecond light source and the second detecting means are integrallyprovided as a second unit.
 15. An optical head according to claim 6,wherein the first light beam has a first polarization direction and thesecond light beam has a second polarization direction, and wherein thefirst and second light sources are positioned so that the firstpolarization direction is substantially perpendicular to the secondpolarization direction.
 16. An optical head according to claim 15,wherein the combining means transmits one of the first and second lightbeams and reflects the other in accordance with polarization directionsof the first and second light beams, so as to guide the first and secondlight beams to the optical system.
 17. An optical head according toclaim 10, wherein the separating means transmits one of the first andsecond light beams and reflects the other in accordance withpolarization directions of the first and second light beams.
 18. Anoptical head according to claim 11, wherein the separating meanstransmits one of the first and second light beams and reflects the otherin accordance with polarization directions of the first and second lightbeams.
 19. An optical head according to claim 6, wherein the combiningmeans transmits one of the first and second light beams and reflects theother in accordance with wavelengths of the first and second lightbeams, so as to guide the first and second light beams to the opticalsystem.
 20. An optical head according to claim 10, wherein theseparating means transmits one of the first and second light beams andreflects the other in accordance with wavelengths of the first andsecond light beams.
 21. An optical head according to claim 11, whereinthe separating means transmits one of the first and second light beamsand reflects the other in accordance with wavelengths of the first andsecond light beams.
 22. An optical head according to claim 16, whereinthe combining means transmits one of the first and second light beamsand reflects the other in accordance with wavelengths of the first andsecond light beams, to guide the first and second light beams to theoptical system.
 23. An optical head according to claim 17, wherein theseparating means transmits one of the first and second light beams andreflects the other in accordance with wavelengths of the first andsecond light beams.
 24. An optical head according to claim 18, whereinthe separating means transmits one of the first and second light beamsand reflects the other in accordance with wavelengths of the first andsecond light beams.
 25. An optical head according to claim 3, furthercomprising aperture limiting means for limiting a radius of the secondlight beam.
 26. An optical head according to claim 25, furthercomprising another aperture limiting means for limiting a radius of thefirst light beam.
 27. An optical head according to claim 3, furthercomprising a wave plate, wherein the first light beam has a firstwavelength substantially equal to the first available wavelength of thefirst optical disk, the second light beam has a second wavelengthsubstantially equal to the second available wavelength of the secondoptical disk, and the wave plate gives a phase difference of a quarterwavelength to the first light beam and that of a half wavelength to thesecond light beam.
 28. An optical head according to claim 1, wherein theoptical system has a collimate lens for substantially collimating thefirst light beam and an objective lens for converging the collimatedfirst light beam onto the first optical disk.
 29. An optical headaccording to claim 1, wherein the optical system includes an objectivelens and a collimate lens.
 30. An optical head according to claim 26,wherein the optical system includes an objective lens for converging thefirst light beam and the second light beam onto the first optical diskand the second optical disk, respectively, and objective lens movingmeans for moving the objective lens, and wherein the another aperturelimiting means is attached to the objective lens moving means.
 31. Anoptical head according to claim 30, wherein the aperture limiting meansadjusts the radius of the second light beam to be smaller than theradius of the first light beam adjusted by the another aperture limitingmeans.
 32. An optical head according to claim 13, wherein the first unitfurther includes first diffraction means for diffracting the first lightbeam emitted from the first light source so as to generate a pluralityof diffracted beams.
 33. An optical head according to claim 32, whereinthe first diffraction means comprises e diffraction grating having aring shape.
 34. An optical head according to claim 33, wherein theplurality of the diffracted beams include a 0th order diffracted beamand the diffraction grating has a transmittance of the 0th orderdiffracted beam of 10% or less.
 35. An optical head according to claim34, wherein the first unit further includes means for diffracting thefirst light beam reflected by the first optical disk, and wherein thereflected first light beam is incident onto the first detecting meanswithout being incident on the diffraction grating having a ring shape.36. An optical head according to claim 14, wherein the second unitfurther includes second diffraction means for diffracting the secondlight beam emitted from the second light source to generate a pluralityof diffracted beams.
 37. An optical head according to claim 36, whereinthe second diffraction means comprises a diffraction grating having aring shape.
 38. An optical head according to claim 37, wherein theplurality of the diffracted beams include a 0th order diffracted beamand the diffraction grating has a transmittance of the 0th orderdiffracted beam of 10% or less.
 39. An optical head according to claim38, wherein the second unit further includes means for diffracting thesecond light beam reflected by the second optical disk, and wherein thereflected second light beam is incident onto the second detecting meanswithout being incident on the diffraction grating having a ring shape.40. An optical head according to claim 1, further comprising:an aperturelimiting means for limiting a diameter of the second light beam so thatthe diameter of the second light beam is smaller than a diameter of thefirst light beam.
 41. An optical head according to claim 40, wherein theoptical system includes an objective lens and a collimate lens, theobjective lens being attached to a moveable section which moves togetherwith the objective lens, and wherein the aperture limiting means isattached to the moveable section.
 42. An optical data recording andreproducing apparatus comprising an optical head for reproducing datafrom first and second optical disks which are different from each otherin at least one of a base material thickness and an availablewavelength, disk discriminating means for discriminating between thefirst and second optical disks, and drive means for driving the opticalhead based on a result of the discrimination obtained by the diskdiscriminating means, the optical head including:a first light sourcefor emitting a first light beam, the first light beam being used forreproducing data from the first optical disk; an optical system designedto converge the first light beam onto the first optical disk inaccordance with a base material thickness and an available wavelength ofthe first optical disk; and a second light source for emitting a secondlight beam, the second light beam being used for reproducing data fromthe second optical disk, wherein an optical path length between thesecond light source and the optical system is different from an opticalpath length between the first light source and the optical system, thedifference between the optical path length from the first light sourceto the optical system and the optical path length from the second lightsource to the optical system compensating a wave-front aberration due tothe differences in the at least one of the base material thickness andthe available wavelength of the first and the second optical disks, andthe optical system is determined so that the second light beam isconverged onto the second optical disk.